currently I am having an issue retrieving all information via Google Sheets about our Facebook Insights Data. What could be the issue?
It's likely due to a known issue with the default post end-point. We have a fix for that for Sheets and it is described in this article:
If you are actually talking about Facebook Ads connector, then please clarify what element you are trying to get (example of the item in the business manager UI is helpful for me to check if it's in API).